How to unjailbreak my iPhone 4 CDMA tethered?

Hi, I tether jailbroke my iOS 6.1.3 CDMA iPhone 4 and want to unjailbreak it. Every time I go to restore it, my computer says something about the phone not being eligible for the requested build. I'm currently trying to do the "Erase all content and settings" then, when it's done, I'm gonna try to restore it again. Does anyone else know how to solve this issue? Answers are greatly appreciated. Thank you.

Added (1). Basically I tried to restore it and that's what came up…

You're pretty much screwed the only way you can do it is if you restore it

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